Binary multileaf collimator delivery with per-leaf field width

ABSTRACT

A radiation treatment delivery system, includes a linear accelerator (LINAC) and a multileaf collimator (MLC), coupled with the distal end of the LINAC, wherein the MLC has two banks of leaves, organized into a plurality of opposing leaf pairs. The system further includes a processing device, operatively coupled to the LINAC and the MLC, to control the plurality of leaf pairs of the MLC such that for each of a plurality of radiation beam delivery positional sections corresponds to a range of radiation beam positions over a discrete time interval, wherein each leaf pair of the plurality of opposing leaf pairs is open to a fixed opening for a fraction of time in the discrete time interval and closed for the remaining fraction of time in the discrete time interval, while a radiation beam of the radiation treatment system is active.

TECHNICAL FIELD

The present disclosure relates to binary multileaf collimator (MLC)delivery with a per-leaf field width in a radiation treatment system.

BACKGROUND

In radiation treatment, doses of radiation delivered via a radiationtreatment beam from a source outside a patient's body are delivered to atarget region in the body, in order to destroy tumorous cells. Care mustbe taken to minimize the amount of radiation that is delivered tonon-treatment regions while maximizing the amount of radiation deliveredto the intended treatment regions. In radiation treatment, a radiationtreatment beam aperture shapes the radiation treatment beam to conform,as closely as possible, to the intended target region. The radiationtreatment beam aperture is commonly defined by an MLC.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will be understood more fully from the detaileddescription given below and from the accompanying drawings of variousimplementations of the disclosure.

FIG. 1A illustrates a helical radiation delivery system, in accordancewith embodiments described herein.

FIG. 1B illustrates a robotic radiation treatment system that may beused in accordance with embodiments described herein.

FIG. 1C illustrates a c-arm gantry-based radiation treatment system, inaccordance with embodiments described herein.

FIG. 2A illustrates a multileaf MLC to provide a radiation treatmentdose to a target region, in accordance with embodiments describedherein.

FIG. 2B illustrates a bottom view of a multileaf MLC, in accordance withembodiments described herein.

FIG. 2C illustrates a perspective view of a multileaf high-speed MLC, inaccordance with embodiments described herein.

FIG. 2C illustrates a perspective view of a multileaf high-speed MLC, inaccordance with embodiments described herein.

FIG. 2D illustrates a top view of the leaves of a multileaf high-speedMLC, in accordance with embodiments described herein.

FIG. 2E illustrates an exemplary leaf arrangement for a multileafhigh-speed MLC, in accordance with embodiments described herein.

FIGS. 3A-C illustrate exemplary leaf open-time profiles, in accordancewith embodiments described herein.

FIGS. 3D-F illustrate exemplary optimized leaf open-time profiles, inaccordance with embodiments described herein.

FIG. 3G illustrates an exemplary leaf open-time profile thatincorporates a maximum velocity, in accordance with embodimentsdescribed herein.

FIGS. 4A-C illustrate a variety of exemplary leaf arrangementsconforming to a target region, in accordance with embodiments describedherein.

FIG. 5A is a flowchart illustrating a method for fast sliding windowwith a high-speed MLC, in accordance with embodiments described herein.

FIG. 5B is a flowchart illustrating a method for binary MLC deliverywith a per-leaf field width, according to embodiments.

FIG. 6 illustrates examples of different systems that may be used in thegenerating of the performing of radiation treatment, in accordance withembodiments described herein.

DETAILED DESCRIPTION

Described herein are embodiments of methods and apparatus for binary MLCradiation treatment delivery with per-leaf field width. In radiationtreatment systems, opposing banks of leaves of an MLC may be used tocreate one or more patterns that shape a radiation treatment beam toconform to a target region.

For target regions with non-uniform shapes, IMRT can be utilized todeliver more complicated radiation treatment doses. Intensity modulatedradiotherapy (IMRT) includes a variety of radiation treatment techniquesthat, essentially, vary the radiation treatment beam intensity that isdirected at the target region. In IMRT, rather than having the MLC shapethe radiation treatment beam to match a particular outline, the MLC isinstead used to create an array of beam shapes that generate a desiredintensity modulation and a desired 3D dose distribution via overlappingradiation fields of (possibly) different intensities.

In some embodiments, binary MLCs include a plurality of leaf pairs,arranged in two opposing banks. Each bank of leaves is used to form atreatment slice by positioning the leaf in a closed position or openposition with respect to the beam. In some embodiments, thesuperior-inferior (sup-inf) field width (e.g., the width formed by theopenings of the leaf pairs in the MLC) is constant across all leaves ofthe MLC. Disadvantageously, this means that such systems are incapableof conforming the field of the radiation treatment beam to a targetprofile along the length of the target. Due to this limitation, fieldsizes in binary MLCs are generally limited to less than 5 cm. Largerfield sizes would generally be undesirable for treating a majoritynumber of target regions, due to the amount of radiation exposure tonon-target regions.

One solution to the above problems is to use dynamic jaws to betterconform the field to the target region on the superior and inferiorends. Such a technique does not conform the field to the edges of thetarget along its length, however, because the field size is defined bythe jaws and is constant across the entire MLC. Another solution is touse a non-binary, shape-conforming MLC. Such MLCs can be slow, however,which may negatively impact treatment time. Another solution is providedherein.

Advantageously, the embodiments described herein allow an MLC to conformtreatment beam fields to target regions, while minimizing radiationexposure to non-treatment regions. Furthermore, the embodimentsdescribed herein allow for larger field sizes (e.g., larger than 5 cm),which may increase the speed of treatments. Furthermore, the embodimentsdescribed herein allow an MLC to modulate fluence field, not just in theIEC-Xb direction, but also in the IEC-Yb direction, as described herein.Furthermore, the embodiments described herein allow for moreopportunities for modulation in the longitudinal direction. This mayallow treatment plans to have a looser pitch (e.g., close to 1), wheresup-inf modulation is handled by longitudinal modulation of MLC leaves.Alternatively, a tighter pitch may be maintained with additionalopportunities to modulate the treatment beam over the same sup-infregion.

The systems and methods described herein accomplish the above advantagesvia the use of a high-speed MLC. One example, of such a high-speed MLCis an electromagnetic MILC (eMLC), as described herein. It should benoted, however, that alternative variations of a high-speed MLC may beused to perform the operations described herein. For the purposes of thepresent disclosure, a high-speed MLC may be any MLC that is capable ofvery fast leaf motion (e.g., approximately able to cross a 5 cm field inless than 100 ms). It should be noted that although “eMLC” is usedthroughout the present disclosure, the systems and methods describedherein are equally compatible with any other form of high-speed MLC.

Furthermore, for the purposes of this description, the terms “fluence,”“intensity,” and “dose” are used as follows. Fluence is the number ofphotons or x-rays that crosses a unit of area perpendicular to aradiation beam. Fluence rate is the fluence per unit time. Intensity isthe energy that crosses a unit area per unit time. Fluence and intensityare independent of what occurs in a patient, and more specifically arenot dose. Dose is the amount of energy absorbed by tissue by virtue ofradiation impacting the tissue. Radiation dose is measured in units ofgray (Gy), where each Gy corresponds to a fixed amount of energyabsorbed in a unit mass of tissue (e.g., 1 joule/kg). Dose is not thesame as fluence, but increases/decreases as fluence increases/decreases.

The terms “target” and “target region” may refer to one or morefiducials near (within some defined proximity to) a treatment area(e.g., a tumor). In another embodiment, a target may be a bonystructure. In yet another embodiment a target may refer to soft tissueof a patient. A target may be any defined structure or area capable ofbeing identified and tracked, as described herein.

FIG. 1A illustrates a helical radiation delivery system 800 inaccordance with embodiments of the present disclosure. The helicalradiation delivery system 800 may include a linear accelerator (LINAC)850 mounted to a ring gantry 820. The LINAC 850 may be used to generatea radiation beam (i.e., treatment beam) by directing an electron beamtowards an x-ray emitting target. The treatment beam may deliverradiation to a target region (i.e., a tumor). The treatment systemfurther includes a multileaf collimator (MLC) 860 coupled with thedistal end of the LINAC 850. The MLC 860 may be an eMLC, as describedherein. The MLC includes a housing that houses multiple leaves that aremovable to adjust an aperture of the MLC to enable shaping of thetreatment beam. The ring gantry 820 has a toroidal shape in which thepatient 830 extends through a bore of the ring/toroid and the LINAC 850is mounted on the perimeter of the ring and rotates about the axispassing through the center to irradiate a target region with beamsdelivered from one or more angles around the patient. During treatment,the patient 830 may be simultaneously moved through the bore of thegantry on a treatment couch 840.

The helical radiation delivery system 800 includes an imaging system,comprising the LINAC 850 as an imaging source and an x-ray detector 870.The LINAC 850 may be used to generate a mega-voltage x-ray image (MVCT)of a region of interest (ROI) of patient 830 by directing a sequence ofx-ray beams at the ROI which are incident on the x-ray detector 870opposite the LINAC 850 to image the patient 830 for setup and generatepre-treatment images. In one embodiment, the helical radiation deliverysystem 800 may also include a secondary imaging system consisting of akV imaging source 810 mounted orthogonally relative to the LINAC 850(e.g., separated by 90 degrees) on the ring gantry 820 and may bealigned to project an imaging x-ray beam at a target region and toilluminate an imaging plane of a detector after passing through thepatient 130.

FIG. 1B illustrates a radiation treatment system 1200 that may be usedin accordance with alternative embodiments described herein. As shown,FIG. 1B illustrates a configuration of a radiation treatment system1200. In the illustrated embodiments, the radiation treatment system1200 includes a linear accelerator (LINAC) 1201 that acts as a radiationtreatment source and an MLC 1205 (e.g., an eMLC) coupled with the distalend of the LINAC 1201 to shape the treatment beam. In one embodiment,the LINAC 1201 is mounted on the end of a robotic arm 1202 havingmultiple (e.g., 5 or more) degrees of freedom in order to position theLINAC 1201 to irradiate a pathological anatomy (e.g., target) with beamsdelivered from many angles, in many planes, in an operating volumearound a patient. Treatment may involve beam paths with a singleisocenter, multiple isocenters, or with a non-isocentric approach.

LINAC 1201 may be positioned at multiple different nodes (predefinedpositions at which the LINAC 1201 is stopped and radiation may bedelivered) during treatment by moving the robotic arm 1202. At thenodes, the LINAC 1201 can deliver one or more radiation treatment beamsto a target, where the radiation beam shape is determined by the leafpositions in the MLC 1205. The nodes may be arranged in an approximatelyspherical distribution about a patient. The particular number of nodesand the number of treatment beams applied at each node may vary as afunction of the location and type of pathological anatomy to be treated.

In another embodiment, the robotic arm 1202 and LINAC 1201 at its endmay be in continuous motion between nodes while radiation is beingdelivered. The radiation beam shape and 2-D intensity map is determinedby rapid motion of the leaves in the MLC 1205 during the continuousmotion of the LINAC 1201.

The radiation treatment system 1200 includes an imaging system 1210having a processing device 1230 connected with x-ray sources 1203A and1203B (i.e., imaging sources) and fixed x-ray detectors 1204A and 1204B.Alternatively, the x-ray sources 1203A, 1203B and/or x-ray detectors1204A, 1204B may be mobile, in which case they may be repositioned tomaintain alignment with the target, or alternatively to image the targetfrom different orientations or to acquire many x-ray images andreconstruct a three-dimensional (3D) cone-beam CT. In one embodiment,the x-ray sources are not point sources, but rather x-ray source arrays,as would be appreciated by the skilled artisan. In one embodiment, LINAC1201 serves as an imaging source, where the LINAC power level is reducedto acceptable levels for imaging.

Imaging system 1210 may perform computed tomography (CT) such as conebeam CT or helical megavoltage computed tomography (MVCT), and imagesgenerated by imaging system 1210 may be two-dimensional (2D) orthree-dimensional (3D). The two x-ray sources 1203A and 1203B may bemounted in fixed positions on the ceiling of an operating room and maybe aligned to project x-ray imaging beams from two different angularpositions (e.g., separated by 90 degrees) to intersect at a machineisocenter (referred to herein as a treatment center, which provides areference point for positioning the patient on a treatment couch 1206during treatment) and to illuminate imaging planes of respectivedetectors 1204A and 1204B after passing through the patient. In oneembodiment, imaging system 1210 provides stereoscopic imaging of atarget and the surrounding volume of interest (VOI). In otherembodiments, imaging system 1210 may include more or less than two x-raysources and more or less than two detectors, and any of the detectorsmay be movable rather than fixed. In yet other embodiments, thepositions of the x-ray sources and the detectors may be interchanged.Detectors 1204A and 1204B may be fabricated from a scintillatingmaterial that converts the x-rays to visible light (e.g., amorphoussilicon), and an array of CMOS (complementary metal oxide silicon) orCCD (charge-coupled device) imaging cells that convert the light to adigital image that can be compared with a reference image during animage registration process that transforms a coordinate system of thedigital image to a coordinate system of the reference image, as is wellknown to the skilled artisan. The reference image may be, for example, adigitally reconstructed radiograph (DRR), which is a virtual x-ray imagethat is generated from a 3D CT image based on simulating the x-ray imageformation process by casting rays through the CT image.

In one embodiment, IGRT delivery system 1200 also includes a secondaryimaging system 1239. Imaging system 1239 is a Cone Beam ComputedTomography (CBCT) imaging system, for example, the medPhoton ImagingRingSystem. Alternatively, other types of volumetric imaging systems may beused. The secondary imaging system 1239 includes a rotatable gantry 1240(e.g., a ring) attached to an arm and rail system (not shown) that movethe rotatable gantry 1240 along one or more axes (e.g., along an axisthat extends from a head to a foot of the treatment couch 1206. Animaging source 1245 and a detector 1250 are mounted to the rotatablegantry 1240. The rotatable gantry 1240 may rotate 360 degrees about theaxis that extends from the head to the foot of the treatment couch.Accordingly, the imaging source 1245 and detector 1250 may be positionedat numerous different angles. In one embodiment, the imaging source 1245is an x-ray source and the detector 1250 is an x-ray detector. In oneembodiment, the secondary imaging system 1239 includes two rings thatare separately rotatable. The imaging source 1245 may be mounted to afirst ring and the detector 1250 may be mounted to a second ring. In oneembodiment, the rotatable gantry 1240 rests at a foot of the treatmentcouch during radiation treatment delivery to avoid collisions with therobotic arm 1202.

As shown in FIG. 1B, the image-guided radiation treatment system 1200may further be associated with a treatment delivery workstation 150. Thetreatment delivery workstation may be remotely located from theradiation treatment system 1200 in a different room than the treatmentroom in which the radiation treatment system 1200 and patient arelocated. The treatment delivery workstation 150 may include a processingdevice (which may be processing device 1230 or another processingdevice) and memory that modify a treatment delivery to the patient 1225based on a detection of a target motion that is based on one or moreimage registrations, as described herein.

FIG. 1C. Illustrates a C-arm radiation delivery system 1400. In oneembodiment, in the C-arm system 1400 the beam energy of a LINAC may beadjusted during treatment and may allow the LINAC to be used for bothx-ray imaging and radiation treatment. In another embodiment, the system1400 may include an onboard kV imaging system to generate x-ray imagesand a separate LINAC to generate the higher energy therapeutic radiationbeams. The system 1400 includes a gantry 1410, a LINAC 1420, an MLC 1470(e.g., an eMLC) coupled with the distal end of the LINAC 1420 to shapethe beam, and a portal imaging detector 1450. The gantry 1410 may berotated to an angle corresponding to a selected projection and used toacquire an x-ray image of a VOI of a patient 1430 on a treatment couch1440. In embodiments that include a portal imaging system, the LINAC1420 may generate an x-ray beam that passes through the target of thepatient 1430 and are incident on the portal imaging detector 1450,creating an x-ray image of the target. After the x-ray image of thetarget has been generated, the beam energy of the LINAC 1420 may beincreased so the LINAC 1420 may generate a radiation beam to treat atarget region of the patient 1430. In another embodiment, the kV imagingsystem may generate an x-ray beam that passes through the target of thepatient 1430, creating an x-ray image of the target. In someembodiments, the portal imaging system may acquire portal images duringthe delivery of a treatment. The portal imaging detector 1450 maymeasure the exit radiation fluence after the beam passes through thepatient 1430. This may enable internal or external fiducials or piecesof anatomy (e.g., a tumor or bone) to be localized within the portalimages.

Alternatively, the kV imaging source or portal imager and methods ofoperations described herein may be used with yet other types ofgantry-based systems. In some gantry-based systems, the gantry rotatesthe kV imaging source and LINAC around an axis passing through theisocenter. Gantry-based systems include ring gantries having generallytoroidal shapes in which the patient's body extends through the bore ofthe ring/toroid, and the kV imaging source and LINAC are mounted on theperimeter of the ring and rotates about the axis passing through theisocenter. Gantry-based systems may further include C-arm gantries, inwhich the kV imaging source and LINAC are mounted, in a cantilever-likemanner, over and rotates about the axis passing through the isocenter.In another embodiment, the kV imaging source and LINAC may be used in arobotic arm-based system, which includes a robotic arm to which the kVimaging source and LINAC are mounted as discussed above. Aspects of thepresent disclosure may further be used in other such systems such as agantry-based LINAC system, static imaging systems associated withradiation therapy and radiosurgery, proton therapy systems using anintegrated image guidance, interventional radiology and intraoperativex-ray imaging systems, etc.

FIG. 2A illustrates a multileaf collimator (MLC) 31 to provide aradiation treatment dose to a target region, in accordance withembodiments described herein. MLC 31 includes two banks of opposingleaves 33, where each leaf 37 may be positioned continuously across theradiation field. The two banks of leaves 33 are positioned so as tocollimate the beam 30 in the desired shape. In one embodiment, each leaf37 may travel beyond the midpoint of the collimator in order to provideflexibility when achieving the desired collimation. The configurationillustrates fully open (41), partially open (43) and closed (45) leafstates.

In an example of radiation therapy, each gantry angle has one beamassociated with that particular gantry angle, which beam 30 is thencollimated into multiple shapes by an MLC. Treatment beam 30 passesthrough the shaped aperture 47 formed by the leaves 37. The resultingcollimated beam continues onto a target 14 within the patient 38. FIG.2A also illustrates how the treatment beam may be visualized orconceptualized as many different beamlets 49. Leaves 37 of the MLC 31are moved into various positions to achieve desired shapes or aperturesfor specified periods of time to achieve fluence map 51 for thatparticular beam. Modulation of the conceptualized beamlets occurs bysequentially and monotonically moving the leaves into desired positionsto achieve desired shapes or apertures such that the time aconceptualized beamlet is exposed controls the intensity of thatbeamlet. In one embodiment, “monotonic,” as herein, means an orderedsequence of apertures where the sequence is dictated by a continuum fromone aperture to a subsequent aperture, or where individual leavesincrement in one direction during a given series of apertures. In otherwords, a sequence of apertures would be dictated by mechanicallimitations of the MLC, not so much by what may achieve the more optimaltreatment delivery. In one embodiment, a sequence would go from aperture1, then 2 then 3 and so on, and not from 1 to 3 then to 5 then back to2. Rather than use a single conformal shape, the MLC may deliver asequence of shapes. The net amount of radiation received at any givengantry position is based upon the extent to which the different shapespermit the passage or blockage of radiation. As seen in FIG. 2A, theshape of MLC 31 shown does not directly correspond to the beamletintensities of the fluence map 51. As will be appreciated, the depictedfluence map shows the accumulation of intensities for multiple shapesthe MLC has taken for that particular gantry angle.

A common limitation of conventional shaping MLCs is that the leavesdefining the shapes move relatively slowly. Using a large numbers ofshapes, or shapes that require large leaf motions, can result in longerpatient treatments. Likewise, the speed of the leaves can limit theability of conventional shaping-MLC's to deliver time-sensitivetreatments, such as utilizing synchronized motion of delivery components(e.g., gantry, couch, x-ray energy etc.). In part for these reasons,prior 2-D intensity map delivery techniques have been limited to beamsdelivered from static positions. Alternately, prior systems that doallow continuous motion of the radiation source generally only allowsingle aperture shapes or morphing from one aperture shape to another asthe radiation source moves, and do not allowed a 2-D intensity map to bedelivered from each radiation source position.

FIG. 2B illustrates a bottom view of a multileaf MLC 61, in accordancewith embodiments described herein. The binary MLC 61 has a plurality ofleaves 63 arranged in two banks 65, 67. Each bank of leaves is used toform a treatment slice by positioning the leaf in a closed position oropen position with respect to the beam. As shown in FIG. 2B, the leavesmay work in concert to be both open (A), both closed (B), or where onlyone leaf is open/closed (C). In a conventional binary MLC, the leaves 63open (A) to the same, uniform width during an entire single positionalsection. In a conventional shaping MLC, the leaves 63 may open (A) todifferent, various widths during an entire single positional section. Acommon limitation of conventional binary MLCs is that the leaves 63 maynot be open to a variety of different widths for any fraction of timeduring each positional section. Thus, shaping radiation beams to atarget area while simultaneously minimizing radiation exposure tonon-target areas may be difficult. Advantageously, the methods andsystems described herein, allow for the benefits of a shaping MLC (e.g.,the leaves 63 may be open to a variety of different widths for anyfraction of time during each positional section), while maintaining thespeed of a binary MLC.

FIG. 2C illustrates a perspective view of a multileaf high-speed MLC 62,in accordance with embodiments described herein. In one embodiment, aradiation modulation device 34 includes an electromagnetically actuatedMLC (eMLC) 62, which includes a plurality of leaves 66 operable to movefrom position to position, to provide intensity modulation. Leaves 66can move to any position between a minimally and maximally-openposition, with sufficient speed such that leaf sequencing or positioningwill not be significantly influenced by any previous or future positionsof any individual leaf Stated another way, leaf speed is sufficient suchthat the mechanics of the MLC do not unduly influence the determinationof leaf position at any given time for the delivery of a radiationtherapy treatment or fraction. Each leaf 66 is independently controlledby an actuator (not shown, but more fully described below), such as amotor, or magnetic drive in order that leaves 66 are controllably movedfrom fully open, fully closed or to any position between open and closedas described in greater detail below. The actuators can be suitablycontrolled by computer 74 and/or a controller.

In one embodiment, the MLC 62 is coupled with the distal end of theLINAC of a radiation treatment delivery system. A processing device ofthe computer 74 may control the plurality of leaf pairs 66 of the MLC 62such that for each of a plurality of radiation beam delivery positionalsections corresponding to a range of radiation beam positions over adiscrete time interval, each leaf pair of the plurality of opposing leafpairs 66 is open to a fixed opening for a fraction of time in thediscrete time interval and closed for the remaining fraction of time inthe discrete time interval, while a radiation beam of the radiationtreatment system is active. In one embodiment, the fixed opening and thefraction of time form overlapping radiation fields of differentintensities that combine to result in an intensity modulated fluencefield delivered to a treatment target. In one embodiment, the fixedopening conforms to the outline of a treatment target, projected backalong the radiation beam to the MLC, and within a maximum range oftravel of plurality of leaf pairs within the MLC. This concept isfurther described with respect to FIGS. 4A-C and FIG. 5B.

In one embodiment, the processing device of the computer 74 may controlthe MLC 62 to modulate a sub-beam intensity of the radiation beam acrossa plurality of sub-beams that subdivide a fluence field into a 2D grid,and wherein a plurality of independent 2D sub-beam intensity patternsare delivered from a plurality of gantry angles while the gantry movescontinuously. This concept is further described with respect to FIGS.3A-F and FIG. 5A.

In one embodiment, the LINAC including the MLC 62 is mounted on arotating gantry, wherein radiation beams delivered from the range ofradiation beam positions rotate around a treatment target. The treatmenttarget may be moved axially through a bore of the rotating gantry, andthe radiation beams delivered from the range of radiation beam positionsmay follow a helical path about the treatment target. In anotherembodiment, the LINAC and the MLC 62 are mounted on a robotic arm, andthe radiation beam delivered from the range of radiation beam positionsis non-coplanar.

FIG. 2D illustrates a top view of the leaves of a multileaf high-speedMLC 240, in accordance with embodiments described herein. Centralportion 302 of MLC 240 includes inner leaf guides 301, aperture 1050 and14 leaf pairs (1010-1039) in various positions between leaf guide innersupports 301. While 14 leaf pairs are shown, more or fewer leaf pairsmay be provided according to the design requirements of a particularsystem. In one embodiment, there are 64 leaf pairs. In anotherembodiment, there are 96 leaf pairs. In still another embodiment, thereare 32 leaf pairs. As will be apparent, radiation is collimated throughthis section 302 of the collimator.

In FIG. 2D, each leaf is positioned in a particular position to define aparticular aperture or shape 1050, through which radiation may pass,also referred to herein as a state. Leaf pairs 1010 and 1011 through1038 and 1039 are controlled using the control schemes and driversdescribed herein to enable simultaneous volume and intensity modulation.In alternative aspects, one or more controllable jaws are used toprovide primary collimation of the beam, defined by the inner edges 301i and the frames 97A, 97B (i.e., the jaws will block the open spacebetween support frame B and leaf pair 1010/1011 and between supportframe A and leaf pair 1038/1039). Additionally or alternatively, the oneor more pairs of jaws may be adjusted to reduce the size of the primarycollimated beam to smaller than the frame size.

FIG. 2E illustrates an exemplary leaf arrangement for a multileafhigh-speed MLC, in accordance with embodiments described herein. Acollimated field 1040 having a center line 1030 is provided by a pair ofjaws or other collimator device. In the illustrative embodiment, twoleaves form a complementary leaf pair for shaping and modulation of thecollimated field 1040. For example, leaves 1010 and 1011 are one leafpair. Leaves 1018, 1019 are another and leaves 1024, 1025 still another.Each leaf in each pair may be positioned anywhere within field 1040. Theinner edges of each leaf within a leaf pair face each other and maycreate an opening, the collection of openings formed by each leaf pairforms aperture 1050. Aperture 1050 corresponds to an aperture of FIG. 2Dpreviously described and is set according to a treatment plan. In oneembodiment, an aperture 1050 is determined prior to administeringradiation therapy to a patient in the treatment planning process, andoccurs at a particular point during delivery of the treatment plan.Aperture 1050 may change according to a number of factors, such as forexample, the three dimensional shape of the treatment area, intensitymodulation, fluence, and beamlets within a treatment volume, asdescribed herein. Embodiments of the high-speed MLCs described hereinachieve volume and intensity modulation alone, or in simultaneouscombination by providing snap state control.

FIGS. 3A-C illustrate exemplary leaf open-time profiles, in accordancewith embodiments described herein. Unlike using traditional MLCs, byusing an eMLC (or some other suitable high-speed MLC) the amount offluence transmitted at each point along the leaf-pair's direction oftravel (e.g., the IEC-Yb direction) may be precisely controlled, whileat the same time the constantly moving radiation source (e.g., theLINAC) traverses an arc short enough to be considered as one position.To generate a plan for such a high-speed MLC, leaf-open-time profilesmay be determined. In one embodiment, a leaf-open-time profile indicatesthe open time for leaf pairs for a discrete time interval.

To generate an eMLC plan, a leaf-open-time profile for each leaf pair ineach positional section may be divided into discrete beamlets. Anoptimizer may determine an ideal leaf-open-time for each beamlet, asdescribed below. From the leaf-open-time profile, front and backleaf-motion profiles for each leaf pair may be generated, only allowingleaves to move in a single direction in each positional section. In oneembodiment, leaves alternate between moving back-to-front andfront-to-back in successive positional sections, so as a leaf-pairfinishes its travel in one positional section it will be in position tobegin its travel in the next positional section.

FIG. 3A illustrates an example leaf-open-time profile. As shown, theleaf-pair open-times, represented by the bars sitting on the IEC-Ybaxis, may be different for each leaf pair. Note that in the leaf motionprofile algorithm described above, the total time needed to deliver allthe leaf-pair open-times is:

${w(1)} + {\sum\limits_{i = 2}^{n}{\max\{ {{{w(i)} - {w( {i - 1} )}},0} \}}}$Or, equivalently:

${w(n)} + {\sum\limits_{i = 1}^{n - 1}{\max{\{ {{{w(i)} - {w( {i + 1} )}},0} \}.}}}$If this total time is less than the discrete time interval for thepositional section, then the leaf motion profiles may be centered in thepositional section, as shown in FIG. 3B. FIG. 3C illustrates the leadingleaf motion 302 and the trailing leaf motion 304, centered in thepositional section.

FIGS. 3D-F illustrate exemplary optimized leaf open-time profiles, inaccordance with embodiments described herein. In one embodiment, amodulation factor constraint may be applied to the leaf-open-timeprofiles so that the leaf open times are not excessively large (and thusdelay treatment time). To generate the modulation factors, the averagebeamlet open-time is calculated for all non-zero beamlets across allleaves and positional sections. The discrete time interval is thendetermined to be the average open-time, multiplied by the desiredmodulation factor. For each positional section and leaf; beamletopen-times are then adjusted such that the total leaf-open time is nogreater than the discrete time interval corresponding to the positionalsection.

There are several ways to make this adjustment. In one embodiment,individual beamlet open-times that are greater than the discrete timeinterval may be decreased to be equal to the projection time, and thenthe smallest beamlet open-times may be increased until the total leafopen-time is less than or equal to the discrete time interval, asillustrated in FIGS. 3D-F.

FIG. 3G illustrates an exemplary leaf open-time profile thatincorporates a maximum velocity, in accordance with embodimentsdescribed herein. Notably, the leaves of a high-speed MLC move quickly,but not instantaneously. To generate a plan that is actuallydeliverable, leaf motion profiles may account for the finite leaf speedof the MLC. In one embodiment, this can be done by incorporating amaximum leaf velocity (and possibly leaf acceleration) into thegenerated leaf profiles. In one embodiment, the algorithm may strive tokeep the area in each column constant. In the example profile 306,instantaneous leaf motion has been changed to leaf motion with a finitevelocity. Note that the leaf motion in each segment may begin a littleearly, so that the integral open time for the beamlets remainsunaffected. In one embodiment, if the start of travel in the nextprojection overlaps with the end of travel in the current projection,then the leaf may change direction before reaching the end of itstravel, resulting in slightly less fluence being delivered to the targetarea. The operations of FIGS. 3A-G are described further with respect toFIG. 5A.

FIGS. 4A-C illustrate a variety of exemplary leaf arrangementsconforming to a target region 401, in accordance with embodimentsdescribed herein. Each leaf pair is positioned in a particular way suchthat the leaf pair openings define a particular aperture or shape toconform to target region 401. During treatment, radiation passes throughthe aperture defined by the combined leaf pairs, and strikes the targetregion below. A high-speed MLC (e.g., an eMLC), such as that describedherein, opens and closes each leaf pair to an open state or a closedstate during a discrete time interval. Each leaf pair may be open for adifferent fiction of time (e.g., an open-time fraction) during thediscrete time interval, and each leaf pair may be open to a differentwidth during a corresponding open-time fraction. Furthermore, thetreatment beam may be active during the entire discrete time interval.

Advantageously, by activating the treatment beam during the entirediscrete time interval, and allowing each leaf pair to be open for onlya fraction of the discrete time interval to a specified width (which maybe different than widths of other leaf pairs), precise doses ofradiation may be delivered to a variety of complicated target regionshapes. The operations of FIGS. 4A-C are described further with respectto FIG. 5B.

FIG. 5A is a flowchart illustrating a method 500 for fast sliding windowwith a high-speed MLC, in accordance with embodiments described herein.In general, the method 500 may be performed by processing logic that mayinclude hardware (e.g., processing device, circuitry, dedicated logic,programmable logic, microcode, hardware of a device, etc.), software(e.g., instructions run or executed on a processing device), or acombination thereof. In some embodiments, the method 500 may beperformed by processing logic of the radiation treatment system 800 ofFIG. 1A.

As shown in FIG. 5A, the method 500 may begin at block 502 with theprocessing logic shaping, via a collimator mounted to a gantry of aradiation treatment system, a radiation beam directed at a target. Inone embodiment, the collimator is a multileaf collimator (MLC)comprising a plurality of leaf pairs. The MLC may be a high-speed MLC(e.g., an eMLC), as described herein.

Processing logic at block 504 may modulate, by a processing device, asub-beam intensity of the radiation beam across a plurality of sub-beamsthat subdivide a fluence field into a 2D grid. In one embodiment, thesub-beam intensity is modulated by independently modulating a rate oftravel of front and back leaves in each leaf pair, as each leaf pairmoves in a single pass from one end of a corresponding line of travel toanother end of the corresponding line or travel. Additional detailscorresponding to the modulation of sub-beam intensities are providedwith respect to FIGS. 3A-G.

In a variety of embodiments, the 2D grid described herein is arectangular grid. In other embodiments, the 2D grid is any shape. In oneembodiment, a first axis of the 2D sub-beam grid is determined by anindex of the leaf pairs along one axis of the MLC, and a second axis ofthe 2D grid is along a line of travel of the leaf pairs.

Processing logic at block 506 may deliver a plurality of independent 2Dsub-beam intensity patterns from a plurality of gantry angles. In oneembodiment, the plurality of independent 2D sub-beam intensity patternsmay be delivered from a plurality of gantry angles while the gantrymoves continuously. In one embodiment, each of the plurality of leafpairs changes direction when delivering the fluence pattern for eachsubsequent gantry angle.

In one embodiment, processing logic may constrain the motion of theplurality of leaf pairs used to deliver the 2D fluence pattern from aparticular gantry angle to occur in less than a pre-selected time period(as described with respect to FIG. 3D-F). In one embodiment, processinglogic may center leaf pair motion for a particular gantry angle thattakes less than the pre-selected time period within the pre-selectedtime period (as described with respect to FIG. 3A-F). In one embodiment,a first leaf in a leaf pair that follows a second leaf in the leaf pairwhen delivering the intensity pattern from a particular gantry angledoes not reach the end of its travel before reversing direction todeliver the intensity pattern for a subsequent gantry angle (e.g., leafpairs to not need to wait for other leaf pairs to end their travelbefore reversing direction).

In one embodiment, the continuous motion of the gantry may be a helicalmotion. For example, processing logic may rotate the gantrycontinuously, wherein the 2D sub-beam intensity pattern for a particulargantry angle is approximated by delivering the intensity pattern over asmall arc. As used herein, “small arc” may refer to a sub-arc of thetotal gantry rotation that is small enough that it may be treated as asingle gantry angle for the purposes of planning the intended dosedistribution. In one embodiment, “small arc” may refer to approximately7 degrees around the total gantry rotation. In other embodiments, otherarc sizes may be used to deliver one-dimensional beamlet intensitypatterns.

In one embodiment, processing logic moves the target axially through acenter of the gantry via an axial support (e.g., a treatment couch),wherein the gantry and axial support move simultaneously duringirradiation of the target to perform a helical delivery. In oneembodiment, the helical pitch during the irradiation of the target isgreater than or equal to 0.5. In other embodiments, other helicalpitches greater than or less than 0.5 may be used.

FIG. 5B is a flowchart illustrating a method 501 for binary MLC deliverywith a per-leaf field width, according to embodiments. In general, themethod 501 may be performed by processing logic that may includehardware (e.g., processing device, circuitry, dedicated logic,programmable logic, microcode, hardware of a device, etc.), software(e.g., instructions run or executed on a processing device), or acombination thereof. In some embodiments, the method 501 may beperformed by processing logic of the radiation treatment system 800 ofFIG. 1A.

As shown in FIG. 5B, the method 501 may begin at block 503 with theprocessing logic determining a plurality of radiation beam deliverypositional sections to contain MLC leaf control instructions while aradiation beam is active. In one embodiment, as described herein, eachof the plurality of radiation beam delivery positional sectionscorresponds to a range of radiation beam positions over a discrete timeinterval (e.g., along an arc of a gantry of the radiation treatmentsystem). For example, the radiation beam delivery positional sections(e.g., projections) may correspond to the radiation beam being deliveredfrom at least one of a different position or a different direction.

In other words, the positional sections may be thought of as positionalnodes, from which a LINAC may deliver a radiation treatment beam in aparticular direction. The positional sections may include a range ofpositions (e.g. a zone). For example, an arc in a helical treatmentdelivery system may be divided into a plurality of discrete positionalsections (e.g., where each positional section includes some number ofdegrees around the arc). In one embodiment, a positional section mayinclude approximately seven degrees around an arc (e.g., seven degreesof gantry rotation). In other, non-helical embodiments, positionalsections may be defined in terms of three-dimensional spaces. In oneembodiment, the different direction remains constant while the differentposition follows a linear trajectory that sweeps the radiation beam overa length of a treatment target. In one embodiment, the differentdirections are non-coplanar.

At block 505, processing logic generates a plurality of openings foreach of the plurality of radiation beam delivery positional sections,each of the plurality of openings corresponding to one of a plurality ofleaf pairs of the MLC. Advantageously, each of the plurality of openingsfor each of the plurality of positional sections may correspond to adifferent width. For example, in one embodiment, two or more of theplurality of openings correspond to different widths in the samepositional section. In one embodiment, the plurality of openings conformto an outline of a treatment target, projected back along the radiationbeam to the MLC, and within a maximum range of travel of the pluralityof leaf pairs within the MLC.

At block 507, processing logic generates a plurality of leaf open-timefractions for each of the plurality of radiation beam deliverypositional sections, each of the plurality of leaf open-time fractionscorresponding to one of the plurality of leaf pairs of the MLC. In oneembodiment, leaf open-time fractions are discrete amounts of time thatare less than the discrete time interval. In another embodiment, a leafopen-time fraction may be a discrete amount of time that is equal to thediscrete time interval. Advantageously, leaf open-time fractions alloweach of the plurality of leaf pairs to be open for a different amount oftime during the discrete time interval. For example, in the presentembodiment, two or more of the plurality of leaf open-time fractionsduring the discrete time interval may be different.

At block 509, processing logic controls, by a processing device, theplurality of leaf pairs of the MLC such that each leaf pair of theplurality of leaf pairs is opened to a corresponding opening of theplurality of openings for a corresponding leaf open-time fraction of theplurality of leaf open-time fractions during the discrete time intervalcorresponding to the range of radiation beam positions, while theradiation beam of the radiation treatment system is active. In oneembodiment, the treatment beam is active during the entire discrete timeinterval (e.g., as the LINAC travels through the positional section).

In one embodiment, the plurality of leaf open-time fractions formoverlapping radiation fields of different intensities that combine toresult in an intensity modulated fluence field delivered to a treatmenttarget. Advantageously, the above operations allow a radiation treatmentdelivery system to effectively time-modulate a radiation treatment beamwhile precisely conforming to the outline of a target area.

FIG. 6 illustrates examples of different systems 600 within which a setof instructions, for causing the systems to perform any one or more ofthe methodologies discussed herein, may be executed. In alternativeimplementations, the machine may be connected (e.g., networked) to othermachines in a LAN, an intranet, an extranet, and/or the Internet. Eachof the systems may operate in the capacity of a server or a clientmachine in client-server network environment, as a peer machine in apeer-to-peer (or distributed) network environment, or as a server or aclient machine in a cloud computing infrastructure or environment.

The systems are machines capable of executing a set of instructions(sequential or otherwise) that specify actions to be taken by thatmachine. Further, while a single machine is illustrated, the term“machine” shall also be taken to include any collection of machines thatindividually or jointly execute a set (or multiple sets) of instructionsto perform any one or more of the methodologies discussed herein.

As described below and illustrated in FIG. 6, a system 600 may include adiagnostic imaging system 605, a treatment planning system 610, and atreatment delivery system 615. Diagnostic imaging system 605 may be anysystem capable of producing medical diagnostic images of a patient thatmay be used for subsequent medical diagnosis, treatment planning,treatment simulation and/or treatment delivery. For example, diagnosticimaging system 605 may be a computed tomography (CT) system, a magneticresonance imaging (MRI) system, a positron emission tomography (PET)system, a combination of such systems, or the like. For ease ofdiscussion, diagnostic imaging system 605 may be discussed below attimes in relation to an x-ray imaging modality. In other embodiments,other imaging modalities such as those discussed above may also be used.

In one embodiment, diagnostic imaging system 605 includes an imagingsource 620 to generate an imaging beam (e.g., x-rays) and an imagingdetector 630 to detect and receive the beam generated by imaging source620, or a secondary beam or emission stimulated by the beam from theimaging source (e.g., in an MRI or PET scan).

In one embodiment, imaging source 620 and imaging detector 630 may becoupled to a digital processing system 625 to control the imagingoperation and process image data. In one embodiment, diagnostic imagingsystem 605 may receive imaging commands from treatment delivery system615 and/or treatment planning system 610.

Diagnostic imaging system 605 includes a bus or other means 680 fortransferring data and commands among digital processing system 625,imaging source 620 and imaging detector 630. Digital processing system625 may include one or more general-purpose processors (e.g., amicroprocessor), special purpose processor such as a digital signalprocessor (DSP) or other type of processing device such as a controlleror field programmable gate array (FPGA). Digital processing system 625may also include other components (not shown) such as memory, storagedevices, network adapters and the like. Digital processing system 625may be configured to generate digital diagnostic images in a standardformat, such as the Digital Imaging and Communications in Medicine(DICOM) format, for example. In other embodiments, digital processingsystem 625 may generate other standard or non-standard digital imageformats. Digital processing system 625 may transmit diagnostic imagefiles (e.g., the aforementioned DICOM formatted files) to treatmentdelivery system 615 over a data link 683, which may be, for example, adirect link, a local area network (LAN) link or a wide area network(WAN) link such as the Internet. In addition, the informationtransferred between systems may either be pulled or pushed across thecommunication medium connecting the systems, such as in a remotediagnosis or treatment planning configuration. In remote diagnosis ortreatment planning, a user may utilize embodiments of the presentdisclosure to diagnose or treat a patient despite the existence of aphysical separation between the system user and the patient.

In one embodiment, treatment delivery system 615 includes a therapeuticand/or surgical radiation source 660 to administer a prescribedradiation dose to a target volume in conformance with a treatment plan.Treatment delivery system 615 may also include imaging system 665 toperform computed tomography (CT) such as cone beam CT, and imagesgenerated by imaging system 665 may be two-dimensional (2D) orthree-dimensional (3D).

Treatment delivery system 615 may also include a digital processingsystem 670 to control radiation source 660, receive and process datafrom diagnostic imaging system 605 and/or treatment planning system 610,and control a patient support device such as a treatment couch 675.Digital processing system 670 may be connected to or a part of a camerafeedback system. Digital processing system 670 may be configured toperform any of the operations described herein. Digital processingsystem 670 may include a processing device that represents one or moregeneral-purpose processors (e.g., a microprocessor), special purposeprocessor such as a digital signal processor (DSP) or other type ofdevice such as a controller or field programmable gate array (FPGA). Theprocessing device of digital processing system 670 may be configured toexecute instructions to perform the operations described herein.

In one embodiment, digital processing system 670 includes system memorythat may include a random access memory (RAM), or other dynamic storagedevices, coupled to a processing device, for storing information andinstructions to be executed by the processing device. The system memoryalso may be used for storing temporary variables or other intermediateinformation during execution of instructions by the processing device.The system memory may also include a read only memory (ROM) and/or otherstatic storage device for storing static information and instructionsfor the processing device.

Digital processing system 670 may also include a storage device,representing one or more storage devices (e.g., a magnetic disk drive oroptical disk drive) for storing information and instructions. Thestorage device may be used for storing instructions for performing thetreatment delivery steps discussed herein. Digital processing system 670may be coupled to radiation source 660 and treatment couch 675 by a bus692 or other type of control and communication interface.

In one embodiment, the treatment delivery system 615 includes an inputdevice 678 and a display 677 connected with digital processing system670 via bus 692. The display 677 can show trend data that identifies arate of target movement (e.g., a rate of movement of a target volumethat is under treatment). The display can also show a current radiationexposure of a patient and a projected radiation exposure for thepatient. The input device 678 can enable a clinician to adjustparameters of a treatment delivery plan during treatment.

Treatment planning system 610 includes a processing device 640 togenerate and modify treatment plans and/or simulation plans. Processingdevice 640 may represent one or more general-purpose processors (e.g., amicroprocessor), special purpose processor such as a digital signalprocessor (DSP) or other type of device such as a controller or fieldprogrammable gate array (FPGA). Processing device 640 may be configuredto execute instructions for performing simulation generating operationsand/or treatment planning operations discussed herein.

Treatment planning system 610 may also include system memory 635 thatmay include a random access memory (RAM), or other dynamic storagedevices, coupled to processing device 640 by bus 686, for storinginformation and instructions to be executed by processing device 640.System memory 635 also may be used for storing temporary variables orother intermediate information during execution of instructions byprocessing device 640. System memory 635 may also include a read onlymemory (ROM) and/or other static storage device coupled to bus 686 forstoring static information and instructions for processing device 640.

Treatment planning system 610 may also include storage device 645,representing one or more storage devices (e.g., a magnetic disk drive oroptical disk drive) coupled to bus 686 for storing information andinstructions. Storage device 645 may be used for storing instructionsfor performing the treatment planning steps discussed herein.

Processing device 640 may also be coupled to a display device 650, suchas a cathode ray tube (CRT) or liquid crystal display (LCD), fordisplaying information (e.g., a 2D or 3D representation of the VOI) tothe user. An input device 655, such as a keyboard, may be coupled toprocessing device 640 for communicating information and/or commandselections to processing device 640. One or more other user inputdevices (e.g., a mouse, a trackball or cursor direction keys) may alsobe used to communicate directional information, to select commands forprocessing device 640 and to control cursor movements on display 650.

Treatment planning system 610 may share its database (e.g., data storedin storage 645) with a treatment delivery system, such as treatmentdelivery system 615, so that it may not be necessary to export from thetreatment planning system prior to treatment delivery. Treatmentplanning system 610 may be linked to treatment delivery system 615 via adata link 690, which in one embodiment may be a direct link, a LAN linkor a WAN link.

It should be noted that when data links 683, 686, and 690 areimplemented as LAN or WAN connections, any of diagnostic imaging system605, treatment planning system 610 and/or treatment delivery system 615may be in decentralized locations such that the systems may bephysically remote from each other. Alternatively, any of diagnosticimaging system 605, treatment planning system 610, and/or treatmentdelivery system 615 may be integrated with each other in one or moresystems.

It will be apparent from the foregoing description that aspects of thepresent disclosure may be embodied, at least in part, in software. Thatis, the techniques may be carried out in a computer system or other dataprocessing system in response to a processing device 625, 640, or 670(see FIG. 6), for example, executing sequences of instructions containedin a memory. In various implementations, hardware circuitry may be usedin combination with software instructions to implement the presentdisclosure. Thus, the techniques are not limited to any specificcombination of hardware circuitry and software or to any particularsource for the instructions executed by the data processing system. Inaddition, throughout this description, various functions and operationsmay be described as being performed by or caused by software code tosimplify description. However, those skilled in the art will recognizewhat is meant by such expressions is that the functions result fromexecution of the code by processing device 625, 640, or 670.

A machine-readable medium can be used to store software and data whichwhen executed by a general purpose or special purpose data processingsystem causes the system to perform various methods of the presentdisclosure. This executable software and data may be stored in variousplaces including, for example, system memory and storage or any otherdevice that is capable of storing at least one of software programs ordata. Thus, a machine-readable medium includes any mechanism thatprovides (i.e., stores) information in a form accessible by a machine(e.g., a computer, network device, personal digital assistant,manufacturing tool, any device with a set of one or more processors,etc.). For example, a machine-readable medium includesrecordable/non-recordable media such as read only memory (ROM), randomaccess memory (RAM), magnetic disk storage media, optical storage media,flash memory devices, etc. The machine-readable medium may be anon-transitory computer readable storage medium.

Unless stated otherwise as apparent from the foregoing discussion, itwill be appreciated that terms such as “receiving,” “positioning,”“performing,” “emitting,” “causing,” or the like may refer to theactions and processes of a computer system, or similar electroniccomputing device, that manipulates and transforms data represented asphysical (e.g., electronic) quantities within the computer system'sregisters and memories into other data similarly represented as physicalwithin the computer system memories or registers or other suchinformation storage or display devices. Implementations of the methodsdescribed herein may be implemented using computer software. If writtenin a programming language conforming to a recognized standard, sequencesof instructions designed to implement the methods can be compiled forexecution on a variety of hardware platforms and for interface to avariety of operating systems. In addition, implementations of thepresent disclosure are not described with reference to any particularprogramming language. It will be appreciated that a variety ofprogramming languages may be used to implement implementations of thepresent disclosure.

It should be noted that the methods and apparatus described herein arenot limited to use only with medical diagnostic imaging and treatment.In alternative implementations, the methods and apparatus herein may beused in applications outside of the medical technology field, such asindustrial imaging and non-destructive testing of materials. In suchapplications, for example, “treatment” may refer generally to theeffectuation of an operation controlled by the treatment planningsystem, such as the application of a beam (e.g., radiation, acoustic,etc.) and “target” may refer to a non-anatomical object or area.

In the foregoing specification, the disclosure has been described withreference to specific exemplary implementations thereof. It will,however, be evident that various modifications and changes may be madethereto without departing from the broader spirit and scope of thedisclosure as set forth in the appended claims. The specification anddrawings are, accordingly, to be regarded in an illustrative senserather than a restrictive sense.

What is claimed is:
 1. A method of controlling a two-bank multileafcollimator (MLC) of a radiation treatment delivery system, comprising:determining a plurality of radiation beam delivery positional sectionsto contain MLC leaf control instructions while a radiation beam isactive, wherein each of the plurality of radiation beam deliverypositional sections corresponds to a range of radiation beam positionsover a discrete time interval, wherein the discrete time interval isbased on an average open-time and a modulation factor; generating aplurality of openings for each of the plurality of radiation beamdelivery positional sections, each of the plurality of openingscorresponding to one of a plurality of leaf pairs of the MLC, whereintwo or more of the plurality of openings correspond to different widths;generating a plurality of leaf open-time fractions for each of theplurality of radiation beam delivery positional sections, each of theplurality of leaf open-time fractions corresponding to one of theplurality of leaf pairs of the MLC; and controlling, by a processingdevice, the plurality of leaf pairs of the MLC such that each leaf pairof the plurality of leaf pairs is opened to a corresponding opening ofthe plurality of openings for a corresponding leaf open-time fraction ofthe plurality of leaf open-time fractions during the discrete timeinterval corresponding to the range of radiation beam positions, whilethe radiation beam of the radiation treatment system is active.
 2. Themethod of claim 1, wherein the plurality of radiation beam deliverypositional sections corresponds to the radiation beam delivered from atleast one of: a different position or a different direction.
 3. Themethod of claim 1, wherein two or more of the plurality of leafopen-time fractions during the discrete time interval are different. 4.The method of claim 2, wherein the different direction remains constantwhile the different position follows a linear trajectory that sweeps theradiation beam over a length of a treatment target.
 5. The method ofclaim 2, wherein the different directions are non-coplanar.
 6. Themethod of claim 2, wherein the plurality of openings and the pluralityof leaf open-time fractions form overlapping radiation fields ofdifferent intensities that combine to result in an intensity modulatedfluence field delivered to a treatment target.
 7. The method of claim 1,wherein the plurality of openings conform to an outline of a treatmenttarget, projected back along the radiation beam to the MLC, and within amaximum range of travel of the plurality of leaf pairs within the MLC.8. The method of claim 1, wherein the range of radiation beam positionsis along an arc of a gantry of the radiation treatment system.
 9. Themethod of claim 8, wherein the arc corresponds to approximately sevendegrees of gantry rotation.
 10. A radiation treatment delivery system,comprising: a linear accelerator (LINAC) to output a radiation beam at adistal end; a multileaf collimator (MLC), coupled with the distal end ofthe LINAC, wherein the MLC has two banks of leaves, organized into aplurality of opposing leaf pairs; and a processing device, operativelycoupled to the LINAC and the MLC, to: control the plurality of leafpairs of the MLC such that for each of a plurality of radiation beamdelivery positional sections corresponding to a range of radiation beampositions over a discrete time interval, wherein each leaf pair of theplurality of opposing leaf pairs is open to a fixed opening for afraction of time in the discrete time interval and closed for theremaining fraction of time in the discrete time interval, while theradiation beam of the radiation treatment system is active, wherein thediscrete time interval is based on an average open-time and a modulationfactor.
 11. The system of claim 10, wherein the MLC is anelectromagnetically actuated multileaf collimator (eMLC).
 12. The systemof claim 10, wherein the LINAC is mounted on a rotating gantry, andwherein radiation beams delivered from the range of radiation beampositions rotate around a treatment target.
 13. The system of claim 12,wherein the treatment target is moved axially through a bore of therotating gantry, and wherein the radiation beams delivered from therange of radiation beam positions follow a helical path about thetreatment target.
 14. The system of claim 10, wherein the LINAC and theMLC are mounted on a robotic arm, and wherein the radiation beamdelivered from the range of radiation beam positions is non-coplanar.15. The system of claim 10, wherein the fixed opening and the fractionof time form overlapping radiation fields of different intensities thatcombine to result in an intensity modulated fluence field delivered to atreatment target.
 16. The system of claim 10, wherein the fixed openingconforms to an outline of a treatment target, projected back along theradiation beam to the MLC, and within a maximum range of travel ofplurality of leaf pairs within the MLC.
 17. The system of claim 10,wherein the plurality of radiation beam delivery positional sectionscorresponds to the radiation beam delivered from at least one of: adifferent position or a different direction, and wherein the at leastone of: the different position or the different direction follows ahelical trajectory about a treatment target.
 18. The system of claim 10,wherein the system is a helical radiation treatment delivery system. 19.The system of claim 10, wherein the system is a robotic-based LINACradiation treatment system.
 20. The system of claim 10, wherein thesystem is gantry-based radiation treatment delivery system.
 21. Anon-transitory computer readable medium comprising instructions that,when executed by a processing device of a radiation treatment deliverysystem, cause the processing device to: generate a plurality ofradiation beam delivery positional sections to contain MLC leaf controlinstructions while a radiation beam is active, wherein each of theplurality of radiation beam delivery positional sections corresponds toa range of radiation beam positions over a discrete time interval,wherein the discrete time interval is based on an average open-time anda modulation factor; generate a plurality of openings for each of theplurality of radiation beam delivery positional sections, each of theplurality of openings corresponding to one of a plurality of leaf pairsof the MLC; generate a plurality of leaf open-time fractions for each ofthe plurality of radiation beam delivery positional sections, each ofthe plurality of leaf open-time fractions corresponding to one of theplurality of leaf pairs of the MLC; and control, by the processingdevice, the plurality of leaf pairs of the MLC such that each leaf pairof the plurality of leaf pairs is opened to a corresponding opening ofthe plurality of openings for a corresponding leaf open-time fraction ofthe plurality of leaf open-time fractions during the discrete timeinterval corresponding to the range of radiation beam positions, whilethe radiation beam of the radiation treatment system is active.
 22. Thenon-transitory computer readable medium of claim 21, wherein theplurality of radiation beam delivery positional sections corresponds tothe radiation beam delivered from at least one of: a different positionor a different direction.
 23. The non-transitory computer readablemedium of claim 22, wherein the at least one of: the different positionor the different direction follows a helical trajectory about atreatment target.
 24. The non-transitory computer readable medium ofclaim 22, wherein the different direction remains constant while thedifferent position follows a linear trajectory that sweeps the radiationbeam over a length of a treatment target.
 25. The non-transitorycomputer readable medium of claim 22, wherein the different directionsare non-coplanar.
 26. The non-transitory computer readable medium ofclaim 21, wherein the plurality of openings and the plurality of leafopen-time fractions form overlapping radiation fields of differentintensities that combine to result in an intensity modulated fluencefield delivered to a treatment target.
 27. The non-transitory computerreadable medium of claim 21, wherein the plurality of openings conformto an outline of a treatment target, projected back along the radiationbeam to the MLC, and within a maximum range of travel of the pluralityof leaf pairs within the MLC.
 28. The non-transitory computer readablemedium of claim 21, wherein the range of radiation beam positions isalong an arc of a gantry of the radiation treatment system.
 29. Thenon-transitory computer readable medium of claim 28, wherein the arccorresponds to approximately seven degrees of gantry rotation.